I enjoy playing McCree, Roadhog, and Junkrat, i am decent with them as well. But i suck when using their ults, some more than others. Roadhog doesn't suffer as much as the other two does with me though.
McCree i never seem to get more than 1 kill with it, assuming i use it at all. More often than not i end up canceling it because there weren't any targets or they all hid.
Junkrat, i occasionally get kills with his ult, but it always seems to die before i actually get a chance to blow it up. As if they know exactly where its coming from and they all focus it down.
Their ults are just a part of their kid, i am decent with aim and their other abilities though. Would you avoid characters that you are decent with and enjoy playing but cant use their ults to save your life? How would you get better at using them?